We got this in our inbox today. It says it's an exclusive offer for JetBlue American Express Cardholders, however we tried to book a fare using the promo code and it appears to let us use any credit card and still get the savings.
Here's what the offer states: "Reserve that trip you've been planning at the right time and get an extra 15% off your future flight! Just book any JetBlue flight (using promo code AMEX15) between March 12 and March 24, 2009, for travel between May 4 and June 17, 2009, and you'll receive 15% off. This is an exclusive offer for JetBlue Cardmembers, so grab your Card and bring home more rewards.(6) (Blackout dates: 5/21/09 - 5/25/09.) Book here and just plug in the promo code in the Promo Code? box.
And more fine print states: "6. Offers end March 24, 2009, at 11:59 PM EST. Promotion/Discount Codes may not be combined. AMEX15 Discount Code is valid for 15% off of one way or roundtrip travel purchased between March 12, 2009, and March 24, 2009, 11:59 PM EST, for travel between May 4, 2009, and June 17, 2009. Blackout dates are between May 21, 2009, and May 25, 2009. Discount will be deducted off of base fare. If Discount Code travel is changed outside of this window or cancelled, discount will be forfeited and you will be responsible for fare difference plus $100 change/cancel fee per person. Cancellations for non-refundable fares are for a JetBlue travel credit only, which is valid for one year. If a reservation is not changed or canceled prior to scheduled departure, all money associated with the reservation is forfeited. Discount may be used only toward newly-booked travel and may not be applied to existing travel or changes to travel. Discount may not be redeemed for cash. Discount may be used only for flight purchase made via jetblue.com. Discount codes are transferable. Discount may not be used in conjunction with other special offers or towards the purchase of a JetBlue Gift Card, Getaways vacation packages, JetBlue Cruise, or already booked flights. All fares must be purchased at time of reservation, and are one-way, and nontransferable. JetBlue reserves the right to deny boarding to passengers without proper documentation. DIRECTV® service is not available on flights outside the continental U.S. Other restrictions apply. ©2009 JetBlue Airways."